The present invention generally relates to methods and apparatuses for evaluating the durability of magnetic disks, and more particularly to a method and an apparatus for evaluating the durability of a magnetic disk which is used in a magnetic disk unit.
In the magnetic disk unit which uses one or more magnetic disks, the so-called Contact Start Stop (CSS) system is employed. According to the CSS system, a head makes contact with a surface of the magnetic disk when the operation of the magnetic disk unit starts and when the operation of the magnetic disk unit ends. For this reason, a protection layer is provided on the surface of the magnetic disk, but still, frictional wear of the magnetic disk occurs due to the contact between the head and the magnetic disk.
On the other hand, due to the increase in the storage capacity and the recording density of the magnetic disk and also due to the decrease in the size of the magnetic disk unit, the floating distance of the head from the magnetic disk is becoming smaller. In addition, in order to prevent the head from being attracted to the surface of the magnetic disk and to ensure floating of the head from the magnetic disk, the surface of the magnetic disk is not perfectly flat and undulations are intentionally formed to a certain extent on the surface of the magnetic disk. As a result, the probability of the head making contact with the magnetic disk has increased.
For this reason, the durability of the magnetic disk has recently become an important factor which affects the performance of the magnetic disk unit. Hence, there are demands to realize a method and an apparatus which can efficiently and accurately evaluate the durability of the magnetic disk.
Conventionally, there is a method which evaluates the durability of the magnetic disk by rotating the magnetic disk at a low speed and preventing the head from floating from the magnetic disk.
In addition, a magnetic disk endurance testing method is proposed in Japanese Laid-Open Patent Application No.63-187422, for example. According to this first proposed method, the magnetic disk which is to be evaluated is rotated under vacuum of 100 mTorr or less, and the head is prevented from floating from the magnetic disk. Thus, the head makes sliding contact with respect to the surface of the magnetic disk, and the durability of the magnetic disk is evaluated by detecting the surface deterioration of the magnetic disk using an acoustic sensor.
Furthermore, a method of evaluating the head floating stability is proposed in Japanese Laid-Open Patent Application No.59-11578, for example. According to this second proposed method, the pressure is decreased in a range of 100 Torr to 1 Torr, and the time it takes for the head to make sliding contact with the surface of the magnetic disk after making contact with the magnetic disk is measured. This measured time is compared with a time which is similarly measured with respect to a standard head, so as to evaluate the head floating stability.
According to the conventional method of evaluating the durability of the magnetic disk described above, however, it takes an extremely long time to check the deterioration of the magnetic disk caused by the sliding contact between the head and the magnetic disk because the magnetic disk is rotated at the low speed. In addition, it is necessary to first clean the surface of the magnetic disk before the deterioration of the magnetic disk can be checked. For this reason, there was a problem in that the durability of the magnetic disk cannot be evaluated efficiently according to the conventional method.
On the other hand, according to the first proposed method described above, the magnetic disk which is to be evaluated is rotated under the vacuum of 100 mTorr or less and the head makes contact with the magnetic disk in this state. Further, the evaluation of the magnetic disk is made under the vacuum of 100 mTorr or less, regardless of the head: and the magnetic disk which are used. Consequently, there were problems in that an expensive apparatus is required to realize the vacuum state of 100 mTorr or less, it takes time to obtain the vacuum state, and the evaluation of the magnetic disk cannot be made within a short time.
Moreover, according to the second proposed method described above, the head makes contact with the magnetic disk which is rotated under the pressure of 100 Torr to 1 Torr. In addition, the evaluation of the magnetic disk is made under the pressure of 100 Torr to 1 Torr, regardless of the head and the magnetic disk which are used. As a result, there were problems in that an expensive apparatus is required to realize the pressure state of 100 Torr to 1 Torr, and although not as long as in the case of the first proposed method, it takes time to obtain the pressure state of 100 Torr to 1 Torr, and the evaluation of the magnetic disk cannot be made within a short time. Furthermore, the object of the second proposed method is to evaluate the head floating stability, and no mention is made of the evaluation of the durability of the magnetic disk.